Matching Items (1,006)
Description
Over the last few decades, homogeneous molybdenum catalysis has been a center of interest to inorganic, organic, and organometallic chemists. Interestingly, most of the important advancements in molybdenum chemistry such as non-classical dihydrogen coordination, dinitrogen reduction, olefin metathesis, and water reduction utilize diverse oxidation states of the metal. However, employment of redox non-innocent ligands to tune the stability and reactivity of such catalysts have been overlooked. With this in mind, the Trovitch group has developed a series of novel bis(imino)pyridine (or pyridine diimine, PDI) and diimine (DI) ligands that have coordinating phosphine or amine arms to exert coordination flexibility to the designed complexes. The research described in this dissertation is focused on the development of molybdenum catalysts that are supported by PDI and DI chelates and their application in small molecule activation.
Using the phosphine containing PDI chelate, Ph2PPrPDI, several low-valent molybdenum complexes have been synthesized and characterized. While the zerovalent monocarbonyl complex, (Ph2PPrPDI)MoCO, catalyzes the reduction of aldehyde C=O bonds, the C-H activated Mo(II) complex, (6-P,N,N,N,C,P-Ph2PPrPDI)MoH was found to be the first well-defined molybdenum catalyst for reducing carbon dioxide to methanol. Along with low- oxidation state compounds, a Mo(IV) complex, [(Ph2PPrPDI)MoO][PF6]2 was also synthesized and utilized in electrocatalytic hydrogen production from neutral water. Moreover, with the proper choice of reductant, an uncommon Mo(I) oxidation state was stabilized and characterized by electron paramagnetic resonance spectroscopy and single crystal X-ray diffraction.
While the synthesized (PDI)Mo complexes unveiled versatile reduction chemistry, varying the ligand backbone to DI uncovered completely different reactivity when bound to molybdenum. Unlike PDI, no chelate-arm C-H activation was observed with the propyl phosphine DI, Ph2PPrDI; instead, a bis(dinitrogen) Mo(0) complex, (Ph2PPrDI)Mo(N2)2 was isolated. Surprisingly, this complex was found to convert carbon dioxide into dioxygen and carbon monoxide under ambient conditions through a novel tail-to-tail CO2 reductive coupling pathway. Detailed experimental and theoretical studies are underway to gain further information about the possible mechanism of Mo mediated direct conversion of CO2 to O2.
Using the phosphine containing PDI chelate, Ph2PPrPDI, several low-valent molybdenum complexes have been synthesized and characterized. While the zerovalent monocarbonyl complex, (Ph2PPrPDI)MoCO, catalyzes the reduction of aldehyde C=O bonds, the C-H activated Mo(II) complex, (6-P,N,N,N,C,P-Ph2PPrPDI)MoH was found to be the first well-defined molybdenum catalyst for reducing carbon dioxide to methanol. Along with low- oxidation state compounds, a Mo(IV) complex, [(Ph2PPrPDI)MoO][PF6]2 was also synthesized and utilized in electrocatalytic hydrogen production from neutral water. Moreover, with the proper choice of reductant, an uncommon Mo(I) oxidation state was stabilized and characterized by electron paramagnetic resonance spectroscopy and single crystal X-ray diffraction.
While the synthesized (PDI)Mo complexes unveiled versatile reduction chemistry, varying the ligand backbone to DI uncovered completely different reactivity when bound to molybdenum. Unlike PDI, no chelate-arm C-H activation was observed with the propyl phosphine DI, Ph2PPrDI; instead, a bis(dinitrogen) Mo(0) complex, (Ph2PPrDI)Mo(N2)2 was isolated. Surprisingly, this complex was found to convert carbon dioxide into dioxygen and carbon monoxide under ambient conditions through a novel tail-to-tail CO2 reductive coupling pathway. Detailed experimental and theoretical studies are underway to gain further information about the possible mechanism of Mo mediated direct conversion of CO2 to O2.
ContributorsPal, Raja (Author) / Trovitch, Ryan J (Thesis advisor) / Buttry, Daniel (Committee member) / Seo, Don (Committee member) / Arizona State University (Publisher)
Created2016
Description
Studying charge transport through single molecules is of great importance for unravelling charge transport mechanisms, investigating fundamentals of chemistry, and developing functional building blocks in molecular electronics.
First, a study of the thermoelectric effect in single DNA molecules is reported. By varying the molecular length and sequence, the charge transport in DNA was tuned to either a hopping- or tunneling-dominated regimes. In the hopping regime, the thermoelectric effect is small and insensitive to the molecular length. Meanwhile, in the tunneling regime, the thermoelectric effect is large and sensitive to the length. These findings indicate that by varying its sequence and length, the thermoelectric effect in DNA can be controlled. The experimental results are then described in terms of hopping and tunneling charge transport models.
Then, I showed that the electron transfer reaction of a single ferrocene molecule can be controlled with a mechanical force. I monitor the redox state of the molecule from its characteristic conductance, detect the switching events of the molecule from reduced to oxidized states with the force, and determine a negative shift of ~34 mV in the redox potential under force. The theoretical modeling is in good agreement with the observations, and reveals the role of the coupling between the electronic states and structure of the molecule.
Finally, conclusions and perspectives were discussed to point out the implications of the above works and future studies that can be performed based on the findings.
First, a study of the thermoelectric effect in single DNA molecules is reported. By varying the molecular length and sequence, the charge transport in DNA was tuned to either a hopping- or tunneling-dominated regimes. In the hopping regime, the thermoelectric effect is small and insensitive to the molecular length. Meanwhile, in the tunneling regime, the thermoelectric effect is large and sensitive to the length. These findings indicate that by varying its sequence and length, the thermoelectric effect in DNA can be controlled. The experimental results are then described in terms of hopping and tunneling charge transport models.
Then, I showed that the electron transfer reaction of a single ferrocene molecule can be controlled with a mechanical force. I monitor the redox state of the molecule from its characteristic conductance, detect the switching events of the molecule from reduced to oxidized states with the force, and determine a negative shift of ~34 mV in the redox potential under force. The theoretical modeling is in good agreement with the observations, and reveals the role of the coupling between the electronic states and structure of the molecule.
Finally, conclusions and perspectives were discussed to point out the implications of the above works and future studies that can be performed based on the findings.
ContributorsLi, Yueqi, Ph.D (Author) / Tao, Nongjian (Thesis advisor) / Buttry, Daniel (Committee member) / Mujica, Vladimiro (Committee member) / Arizona State University (Publisher)
Created2017
Description
This work describes the investigation of novel cathode and anode materials. Specifically, several mixed polyanion compounds were evaluated as cathodes for Li and Na-ion batteries. Clathrate compounds composed of silicon or germanium arranged in cage-like structures were studied as anodes for Li-ion batteries.
Nanostructured Cu4(OH)6SO4 (brochantite) platelets were synthesized using polymer-assisted titration and microwave-assisted hydrothermal methods. These nanostructures exhibited a capacity of 474 mAh/g corresponding to the full utilization of the copper redox in an conversion reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies were preformed to understand the mechanism and structural changes.
A microwave hydrothermal synthesis was developed to prepare a series compounds based on jarosite, AM3(SO4)2(OH)6 (A = K, Na; M = Fe, V). Both the morphology and electrochemical properties showed a compositional dependence. At potentials >1.5 V vs. Li/Li+, an insertion-type reaction was observed in Na,Fe-jarosite but not in K,Fe-jarosite. Reversible insertion-type reactions were observed in both vanadium jarosites between 1 – 4 V with capacities around 40 - 60 mAh/g. Below 1 V vs. Li/Li+, all four jarosite compounds underwent conversion reactions with capacities ~500 mAh/g for the Fe-jarosites.
The electrochemical properties of hydrogen titanium phosphate sulfate, H0.4Ti2(PO4)2.4(SO4)0.6 (HTPS), a new mixed polyanion material with NASICON structure was reported. A capacity of 148 mAh/g corresponding to2 Li+ insertion per formula unit was observed. XRD and XPS were used to characterize the HTPS before and after cycling and to identify the lithium sites. Evaluation of the HTPS in Na-ion cell was also performed, and a discharge capacity of 93 mAh/g was observed.
A systematic investigation of the role of the processing steps, such as ball-milling and acid/base etching, on the electrochemical properties of a silicon clathrate compound with nominal composition of Ba8Al16Si30 was performed. According to the transmission electron microscope (TEM), XPS, and electrochemical analysis, very few Li atoms can be electrochemically inserted, but the introduction of disorder through ball-milling resulted in higher capacity, while the oxidation layer made by the acid/base treatment prevented the reation. The electrochemical property of germanium clathrate was also investigated, unlike the silicon clathrate, the germanium one underwent a conversion reaction.
Nanostructured Cu4(OH)6SO4 (brochantite) platelets were synthesized using polymer-assisted titration and microwave-assisted hydrothermal methods. These nanostructures exhibited a capacity of 474 mAh/g corresponding to the full utilization of the copper redox in an conversion reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies were preformed to understand the mechanism and structural changes.
A microwave hydrothermal synthesis was developed to prepare a series compounds based on jarosite, AM3(SO4)2(OH)6 (A = K, Na; M = Fe, V). Both the morphology and electrochemical properties showed a compositional dependence. At potentials >1.5 V vs. Li/Li+, an insertion-type reaction was observed in Na,Fe-jarosite but not in K,Fe-jarosite. Reversible insertion-type reactions were observed in both vanadium jarosites between 1 – 4 V with capacities around 40 - 60 mAh/g. Below 1 V vs. Li/Li+, all four jarosite compounds underwent conversion reactions with capacities ~500 mAh/g for the Fe-jarosites.
The electrochemical properties of hydrogen titanium phosphate sulfate, H0.4Ti2(PO4)2.4(SO4)0.6 (HTPS), a new mixed polyanion material with NASICON structure was reported. A capacity of 148 mAh/g corresponding to2 Li+ insertion per formula unit was observed. XRD and XPS were used to characterize the HTPS before and after cycling and to identify the lithium sites. Evaluation of the HTPS in Na-ion cell was also performed, and a discharge capacity of 93 mAh/g was observed.
A systematic investigation of the role of the processing steps, such as ball-milling and acid/base etching, on the electrochemical properties of a silicon clathrate compound with nominal composition of Ba8Al16Si30 was performed. According to the transmission electron microscope (TEM), XPS, and electrochemical analysis, very few Li atoms can be electrochemically inserted, but the introduction of disorder through ball-milling resulted in higher capacity, while the oxidation layer made by the acid/base treatment prevented the reation. The electrochemical property of germanium clathrate was also investigated, unlike the silicon clathrate, the germanium one underwent a conversion reaction.
ContributorsZhao, Ran (Author) / Chan, Candace K. (Thesis advisor) / Buttry, Daniel (Committee member) / Yarger, Jeffery (Committee member) / Arizona State University (Publisher)
Created2017
Description
Complex samples, such as those from biological sources, contain valuable information indicative of the state of human health. These samples, though incredibly valuable, are difficult to analyze. Separation science is often used as the first step when studying these samples. Electrophoretic exclusion is a novel separations technique that differentiates species in bulk solution. Due to its ability to isolate species in bulk solution, it is uniquely suited to array-based separations for complex sample analysis. This work provides proof of principle experimental results and resolving capabilities of the novel technique. Electrophoretic exclusion is demonstrated at a single interface on both benchtop and microscale device designs. The benchtop instrument recorded absorbance measurements in a 365 μL reservoir near a channel entrance. Results demonstrated the successful exclusion of a positively-charged dye, methyl violet, with various durations of applied potential (30 - 60 s). This was the first example of measuring absorbance at the exclusion location. A planar, hybrid glass/PDMS microscale device was also constructed. One set of experiments employed electrophoretic exclusion to isolate small dye molecules (rhodamine 123) in a 250 nL reservoir, while another set isolated particles (modified polystyrene microspheres). Separation of rhodamine 123 from carboxylate-modified polystyrene spheres was also shown. These microscale results demonstrated the first example of the direct observation of exclusion behavior. Furthermore, these results showed that electrophoretic exclusion can be applicable to a wide range of analytes. The theoretical resolving capabilities of electrophoretic exclusion were also developed. Theory indicates that species with electrophoretic mobilities as similar as 10-9 cm2/Vs can be separated using electrophoretic exclusion. These results are comparable to those of capillary electrophoresis, but on a very different format. This format, capable of isolating species in bulk solution, coupled with the resolving capabilities, makes the technique ideal for use in a separations-based array.
ContributorsKenyon, Stacy Marie (Author) / Hayes, Mark A. (Thesis advisor) / Ros, Alexandra (Committee member) / Buttry, Daniel (Committee member) / Arizona State University (Publisher)
Created2012
Description
Locomotion of microorganisms is commonly observed in nature. Although microorganism locomotion is commonly attributed to mechanical deformation of solid appendages, in 1956 Nobel Laureate Peter Mitchell proposed that an asymmetric ion flux on a bacterium's surface could generate electric fields that drive locomotion via self-electrophoresis. Recent advances in nanofabrication have enabled the engineering of synthetic analogues, bimetallic colloidal particles, that swim due to asymmetric ion flux originally proposed by Mitchell. Bimetallic colloidal particles swim through aqueous solutions by converting chemical fuel to fluid motion through asymmetric electrochemical reactions. This dissertation presents novel bimetallic motor fabrication strategies, motor functionality, and a study of the motor collective behavior in chemical concentration gradients. Brownian dynamics simulations and experiments show that the motors exhibit chemokinesis, a motile response to chemical gradients that results in net migration and concentration of particles. Chemokinesis is typically observed in living organisms and distinct from chemotaxis in that there is no particle directional sensing. The synthetic motor chemokinesis observed in this work is due to variation in the motor's velocity and effective diffusivity as a function of the fuel and salt concentration. Static concentration fields are generated in microfluidic devices fabricated with porous walls. The development of nanoscale particles that swim autonomously and collectively in chemical concentration gradients can be leveraged for a wide range of applications such as directed drug delivery, self-healing materials, and environmental remediation.
ContributorsWheat, Philip Matthew (Author) / Posner, Jonathan D (Thesis advisor) / Phelan, Patrick (Committee member) / Chen, Kangping (Committee member) / Buttry, Daniel (Committee member) / Calhoun, Ronald (Committee member) / Arizona State University (Publisher)
Created2011
Description
Background: Latinos represent 40.8% of the population in Phoenix (U.S. Census Bureau Population Division, 2010). South Phoenix, also known as the South Mountain Village, defined in geographical terms as area zip codes 85040 and 85042; is a predominantly Latino community comprised of mixed citizenship status households. During the 2010 United States Census 60.3% of the population in South Phoenix identified as Latino, 25.75% of the total population was foreign born. Of the foreign born population, 88.95% were of Latin American origin (United States Census Bureau, 2007-2011 American Community Survey). Understanding how Latino immigrants perceive differences in health between their communities in country of origin and communities in the United States is largely unknown. Irrespective of political positions, understanding how Latino immigrants perceive personal health and the health of their communities is of interest to inform public policy and implement needed interventions in the
public health sphere.
Methods: Semi-structured interviews were collected from 55 adults from the South Phoenix community between November 2009 and September 2010. Interviews were digitally recorded with participant permission and transcribed. Of those collected, 48 transcribed interviews were analyzed using a codebook designed by the researcher. Percent agreement evaluated inter-rater reliability.Results: Latino immigrants in South Phoenix largely agree that health quality is heavily dependent on personal responsibility and not an intrinsic attribute of a given place. Emotional contentedness and distress, both factors of mental health, are impacted by cross-cultural differences between Latino and U.S. culture systems.
Conclusions: As people’s personal perceptions of differences in health are complex concepts influenced by personal backgrounds, culture, and beliefs, attempting to demark a side of the border as ‘healthier’ than the other using personal perceptions is overly simplified and misses central concepts. Instead, exploration of individual variables impacting health allowed this study to gain a more nuanced understanding in how people determine quality of both personal and environmental health. While Latino migrants in South Phoenix largely agree that health is based on personal responsibility and choices, many nonetheless experience higher levels of contentedness and emotional health in their country of origin.
public health sphere.
Methods: Semi-structured interviews were collected from 55 adults from the South Phoenix community between November 2009 and September 2010. Interviews were digitally recorded with participant permission and transcribed. Of those collected, 48 transcribed interviews were analyzed using a codebook designed by the researcher. Percent agreement evaluated inter-rater reliability.Results: Latino immigrants in South Phoenix largely agree that health quality is heavily dependent on personal responsibility and not an intrinsic attribute of a given place. Emotional contentedness and distress, both factors of mental health, are impacted by cross-cultural differences between Latino and U.S. culture systems.
Conclusions: As people’s personal perceptions of differences in health are complex concepts influenced by personal backgrounds, culture, and beliefs, attempting to demark a side of the border as ‘healthier’ than the other using personal perceptions is overly simplified and misses central concepts. Instead, exploration of individual variables impacting health allowed this study to gain a more nuanced understanding in how people determine quality of both personal and environmental health. While Latino migrants in South Phoenix largely agree that health is based on personal responsibility and choices, many nonetheless experience higher levels of contentedness and emotional health in their country of origin.
ContributorsGray, Laurel (Author) / Wutich, Amber (Thesis director) / Quiroga, S. Seline (Committee member) / Nelson, Margaret (Committee member) / Slade, B. Alexandra (Committee member) / Barrett, The Honors College (Contributor) / College of Liberal Arts and Sciences (Contributor)
Created2013-05
Description
Identifying disease biomarkers may aid in the early detection of breast cancer and improve patient outcomes. Recent evidence suggests that tumors are immunogenic and therefore patients may launch an autoantibody response to tumor associated antigens. Single-chain variable fragments of autoantibodies derived from regional lymph node B cells of breast cancer patients were used to discover these tumor associated biomarkers on protein microarrays. Six candidate biomarkers were discovered from 22 heavy chain-only variable region antibody fragments screened. Validation tests are necessary to confirm the tumorgenicity of these antigens. However, the use of single-chain variable autoantibody fragments presents a novel platform for diagnostics and cancer therapeutics.
ContributorsSharman, M. Camila (Author) / Magee, Dewey (Mitch) (Thesis director) / Wallstrom, Garrick (Committee member) / Petritis, Brianne (Committee member) / Barrett, The Honors College (Contributor) / College of Liberal Arts and Sciences (Contributor) / Virginia G. Piper Center for Personalized Diagnostics (Contributor) / Biodesign Institute (Contributor)
Created2012-12
Description
In September 1974, a guerrilla organization called the Montoneros captured Juan and Jorge Born, two Argentinean heirs to a massive food processing conglomerate, and held them for ransom. After months of negotiations between this radical political group and the brothers' family, the Montoneros received $61.5 million dollars for the brothers' re- lease. Other kidnappings followed, netting the revolutionaries close to $100 million dol- lars. Although their tactics initially brought them recognition, they also unleashed a vio- lent response. Through a military coup, General Jorge Videla assumed power and used counterinsurgency tactics against the radical left wing of the Peronist party members. The coming years of military repression put an end to the revolutionary efforts of the Mon- toneros and gave the military leaders a reputation of violators of human rights. Even the Argentine people called the repression the "Dirty War," and investigations estimate that 30,000 people, the Montoneros among them, disappeared.
ContributorsScarvie, Matthew (Author) / Stoner, Kathryn (Thesis director) / Hinojosa, Magda (Committee member) / Mitchell, Michael (Committee member) / Barrett, The Honors College (Contributor) / College of Liberal Arts and Sciences (Contributor)
Created2012-12
Description
While the use of super-cooled gasses as a tool for the study of macroscopic quantum effects has only become experimentally viable in recent years, theories involing such gasses have existed almost as long as quantum theory itself. Albert Einstein first proposed the concept of what is known today as a Bose-Einstein condensate; the driving principle behind his theory was a deliberate exploitation of the symmetric property of multiparticle bosonic wavefunctions. Specifically, since the Bose-Einstein statistics of bosons dic- tate that any arbitrary number of particles can occupy the same state, it is possible in an extremely low energy environment for particles on the order of Avagadro's number to all condense into the ground state. This state of matter is now called a Bose-Einstein condensate (hereafter referred to as a BEC). This state of matter is interesting because having such a large number of particles in the same state allows for the observation of macroscopic quantum effects.
ContributorsSpencer, Kwit (Author) / Schmidt, Kevin (Thesis director) / Treacy, Michael (Committee member) / Dawson, Colby (Committee member) / Barrett, The Honors College (Contributor) / College of Liberal Arts and Sciences (Contributor)
Created2012-12
Description
Organizations use news releases to promote coverage of its operations and enhance the image and issues pertinent to the organization. In most cases, the primary focus of press releases and news media coverage differs. This thesis analyzes the resonance between coverage by news organizations and the materials released by the organization. Analysis of coverage by the news media and the NBA illustrates the resonance and connections in coverage by all three organizations. It also shows how information regarding the NBA lockout released by the NBA and news outlets can be differentiated into unique issue arenas. These issue arenas can have influence on each other, while also allowing organizations to provide their own unique perspectives.
ContributorsEckert, Marshall (Author) / Gilpin, Dawn (Thesis director) / Matera, Fran (Committee member) / Barrett, The Honors College (Contributor) / College of Liberal Arts and Sciences (Contributor) / Walter Cronkite School of Journalism and Mass Communication (Contributor)
Created2012-12